The present invention is directed to a process for the manufacture of branched and optionally crosslinked coatings on bulk polymeric materials with high wettability by aqueous biological media and minimal irreversible adsorption of proteins, and their use for biomedical applications, especially contact lenses including extended-wear contact lenses. The need for highly wettable, minimally protein-fouling coatings is well recognized particularly in the contact lens field. Bulk polymeric materials that possess high oxygen permeability are of great interest for application as extended wear contact lenses. Unfortunately polymers that provide high oxygen transmission possess a relatively hydrophobic surface even if their water content is in the range of 20 to 30%. This leads to excessive discomfort and unacceptably rapid dewetting of the lens by the tear film when such lenses are worn by humans. Hence such contact lens bulk materials must be equipped with a coating that allows good wetting by the human tear fluid. Application of thin polymeric coatings, for instance from gas plasmas (glow discharges) struck in methane/air mixtures ameliorates this problem and enables comfortable wear of such composite lenses. However, the irreversible deposition of biological molecules (biofouling), particularly proteins, onto such coated lenses can lead to the onset of symptoms of discomfort in some wearers and therefore still presents a drawback that needs to be overcome to obtain an ultimately comfortable lens for even the most sensitive wearers.
It is the object of the present invention to provide hydrophilic polymer coatings that have the desirable property of providing superior resistance to fouling of contact lenses by tear film proteins while also allowing high wettability by the tear film. Surprisingly, this can be achieved by the use of branched and optionally crosslinked hydrophilic polymer-containing chains. The coatings of the present invention have been found to result in no observable protein adsorption even when complex multi-protein solutions were used, such as human tear fluid. Exposure to multicomponent protein media presents a far more demanding challenge for coatings intended to be protein-resistant than exposure to single protein solutions, and hence the protein-resisting abilities of the coatings of the present invention are clearly demonstrated.
The present invention therefore in one aspect relates to a process for coating a material surface, comprising the steps of: Coating Process
(a) covalently binding a compound comprising an ethylenically unsaturated double bond to the material surface;
(b) polymerizing a monomer comprising a reactive or crosslinkable group on the surface and thereby providing a primary polymer coating comprising reactive or crosslinkable groups,
(c) in case of a monomer comprising a reactive group in step (b) reacting the reactive groups of the primary coating with a further compound comprising an ethylenically unsaturated double bond and graft-polymerizing a hydrophilic monomer and optionally a co-monomer having a crosslinkable group onto the primary coating obtained according to step (b) and
(d) in case of crosslinkable groups being present in step (b) or (c) initiating crosslinking of said groups.
Examples of materials that may be coated according to the process of the invention are quartz, ceramics, glasses, silicate minerals, silica gels, metals, metal oxides, carbon materials such as graphite or glassy carbon, natural or synthetic organic polymers, or laminates, composites or blends of said materials, in particular natural or synthetic organic polymers which are known in large number. Some examples of polymers are polyaddition and polycondensation polymers (polyurethanes, epoxy resins, polyethers, polyesters, polyamides and polyimides); vinyl polymers (polyacrylates, polymethacrylates, polystyrene, polyethylene and halogenated derivatives thereof, polyvinyl acetate and polyacrylonitrile); elastomers (silicones, polybutadiene and polyisoprene); or modified or unmodified biopolymers (collagen, cellulose, chitosan and the like).
A preferred group of materials to be coated are those being conventionally used for the manufacture of biomedical devices, e.g. contact lenses, in particular contact lenses for extended wear, which are not hydrophilic per se. Such materials are known to the skilled artisan and may comprise for example polysiloxanes, perfluoropolyethers, fluorinated poly(meth)acrylates or equivalent fluorinated polymers derived e.g. from other polymerizable carboxylic acids, polyalkyl (meth)acrylates or equivalent alkylester polymers derived from other polymerizable carboxylic acids, or fluorinated polyolefines, such as fluorinated ethylene propylene, or tetrafluoroethylene, preferably in combination with specific dioxols, such as perfluoro-2,2-dimethyl-1,3-dioxol. Examples of suitable bulk materials are e.g. Lotrafilcon A, Neofocon, Pasifocon, Telefocon, Silafocon, Fluorsilfocon, Paflufocon, Silafocon, Elastofilcon, Fluorofocon or Teflon AF materials, such as Teflon AF 1600 or Teflon AF 2400 which are copolymers of about 63 to 73 mol % of perfluoro-2,2-dimethyl-1,3-dioxol and about 37 to 27 mol % of tetrafluoroethylene, or of about 80 to 90 mol % of perfluoro-2,2-dimethyl-1,3-dioxol and about 20 to 10 mol % of tetrafluoroethylene.
Another preferred group of materials to be coated are those being conventionally used for the manufacture of biomedical devices, e.g. contact lenses, which are hydrophilic per se, since reactive groups, e.g. carboxy, carbamoyl, sulfate, sulfonate, phosphate, amine, ammonium or hydroxy groups, are inherently present in the material and therefore also at the surface of a biomedical device manufactured therefrom. Such materials are known to the skilled artisan and comprise for example polyhydroxyethyl acrylate, polyhydroxyethyl methacrylate (HEMA), polyvinyl pyrrolidone (PVP), polyacrylic acid, polymethacrylic acid, polyacrylamide, polydimethylacrylamide (DMA), polyvinyl alcohol or copolymers for example from two or more monomers from the group hydroxyethyl acrylate, hydroxyethyl methacrylate, N-vinyl pyrrolidone, acrylic acid, methacrylic acid, acrylamide, dimethyl acrylamide, vinyl alcohol and the like. Typical examples are e.g. Polymacon, Tefilcon, Methafilcon, Deltafilcon, Bufilcon, Phemfilcon, Ocufilcon, Focofilcon, Etafilcon, Hefilcon, Vifilcon, Tetrafilcon, Perfilcon, Droxifilcon, Dimefilcon, Isofilcon, Mafilcon, Nelfilcon or Atlafilcon.
Still another group of preferred materials to be coated are amphiphilic segmented copolymers comprising at least one hydrophobic segment and at least one hydrophilic segment which are linked through a bond or a bridge member. Examples are silicone hydrogels, for example those disclosed in PCT applications WO 96/31792 and WO 97/49740 which are herewith incorporated by reference.
The material to be coated may also be any blood-contacting material conventionally used for the manufacture of renal dialysis membranes, blood storage bags, pacemaker leads or vascular grafts. For example, the material to be modified on its surface may be a polyurethane, polydimethylsiloxane, polytetrafluoroethylene, polyvinylchloride, Dacron(trademark) or a composite made therefrom.
Moreover, the material to be coated may also be an inorganic or metallic base material with or without suitable reactive groups, e.g. ceramic, quartz, or metals, such as silicon or gold, or other polymeric or non-polymeric substrates. E.g. for implantable biomedical applications, ceramics or carbohydrate containing materials such as polysaccharides are very useful. In addition, e.g. for biosensor purposes, dextran coated base materials are expected to reduce nonspecific binding effects if the structure of the coating is well controlled. Biosensors may require polysaccharides on gold, quartz, or other non-polymeric substrates. The form of the material to be coated may vary within wide limits. Examples are particles, granules, capsules, fibres, tubes, films or membranes, preferably moldings of all kinds such as ophthalmic moldings, in particular contact lenses.
According to step (a) the compound comprising an ethylenically unsaturated group is suitably covalently bound to the surface of the material to be modified on its surface via reaction of a functional group of the material surface with a co-reactive group of the ethylenically unsaturated compound. Suitable functional groups may be inherently (a priori) present at the surface of the material to be modified on its surface. If substrates contain too few or no reactive groups, the material surface can be modified by methods known per se, for example plasma chemical methods (see, for example, WO 94/06485), or conventional functionalization with groups such as xe2x80x94OH, xe2x80x94NH2 or xe2x80x94CO2H. Suitable functional groups may be selected from a wide variety of groups well known to the skilled artisan. Typical examples are e.g. hydroxy groups, amino groups, carboxy groups, carbonyl groups, aldehyde groups, sulfonic acid groups, sulfonyl chloride groups, isocyanato groups, carboxy anhydride groups, lactone groups, azlactone groups, epoxy groups and groups being replaceable by amino or hydroxy groups, such as halo groups, or mixtures thereof. Amino groups and hydroxy groups are preferred.
The compound comprising an ethylenically unsaturated group according to step (a) may be for example, a vinyl monomer having from 2 to 18 C-atoms and preferably from 2 to 10 C-atoms, which is substituted by a reactive group wherein the above-mentioned meanings and preferences apply.
Suitable reactive groups of the vinyl monomer according to step (a) may be a hydroxy, amino, carboxy, carboxylic acid ester, carboxylic acid anhydride, epoxy, lactone, azlactone or isocyanato group. One group of preferred reactive groups comprises carboxy, carboxylic acid anhydride, azlactone or isocyanato, in particular isocyanato. Another group of preferred reactive groups comprises amino or in particular hydroxy.
Suitable vinyl monomers having a reactive group may be compounds of formula 
wherein R1 is hydrogen, unsubstituted or hydroxy-substituted C1-C6-alkyl or phenyl,
R2 and R3 are each independently of the other hydrogen, C1-C4-alkyl, phenyl, carboxy or halogen,
R4 is hydrogen, C1-C4-alkyl or halogen,
R5 and R5xe2x80x2 are each an ethylenically unsaturated radical having from 2 to 6 C-atoms, or R5 and R5xe2x80x2 together form a bivalent radical xe2x80x94C(R2)xe2x95x90C(R4)xe2x80x94, and
(Alk*) is C1-C6-alkylene, and (Alk**) is C2-C12-alkylene.
The following preferences apply to the variables contained in formulae (1a)-(1e):
R1 is preferably hydrogen or hydroxy-C1-C4-alkyl, in particular hydrogen or xcex2-hydroxyethyl.
One of the variables R2 and R3 is preferably hydrogen and the other one is hydrogen, methyl or carboxy. Most preferably R2 and R3 are each hydrogen.
R4 is preferably hydrogen or methyl.
R5 and R5xe2x80x2 are preferably each vinyl or 1-methylvinyl, or R5 and R5xe2x80x2 together form a radical-C(R2)xe2x95x90C(R4)xe2x80x94 wherein R2 and R4 are each independently hydrogen or methyl. (Alk*) is preferably methylene, ethylene or 1,1-dimethyl-methylene, in particular a radical xe2x80x94CH2xe2x80x94 or xe2x80x94C(CH3)2xe2x80x94.
(Alk**) is preferably C2-C4-alkylene and in particular 1,2-ethylene.
Particularly preferred vinyl monomers having a reactive group are 2-isocyanatoethylmeth-acrylate (IEM), 2-vinyl-azlactone, 2-vinyl-4,4-dimethyl-azlactone, acrylic acid, methacrylic acid, acrylic acid anhydride, maleinic acid anhydride, 2-hydroxyethylacrylate (HEA), 2-hydroxymethacrylate (HEMA), glycidylacrylate or glycidylmethacrylate.
Throughout the application terms such as carboxy, carboxylic acid, xe2x80x94COOH, sulfo, xe2x80x94SO3H, amino, xe2x80x94NH2 and the like always include the free acid or amine as well as a suitable salt thereof, for example a biomedically or in particular occularly acceptable salt thereof such as, for example, a sodium, potassium, ammonium salt or the like (of an acid), or a hydrohalide such a hydrochloride (of an amine).
In a preferred embodiment of the invention, the covalent bonding between the inorganic or preferably material surface and the compound comprising an ethylenically unsaturated group occurs via reaction of a hydroxy, amino, alkylamino, thiol or carboxy group, particularly of a hydroxy or amino group, of the substrate surface with an isocyanato, azlactone, epoxy, carboxy anhydride, carboxy or hydroxy group, particularly with an isocyanato group, of the ethylenically unsaturated compound, for example using an ethylenically unsaturated compound of formula (1a)-(1e). Suitable methods for this are known from textbooks of organic chemistry. The reaction may be carried out, for example, at elevated temperature, for example from 0xc2x0 to 100xc2x0 C. and preferably at room temperature, and optionally in the presence of a catalyst. After the reaction, excess compounds can be removed, for example, with solvents.
According to a preferred embodiment of the invention the material to be coated is an organic polymer containing H-active groups, in particular xe2x80x94OH, xe2x80x94NH2 and/or xe2x80x94NHxe2x80x94, on the surface that are co-reactive with isocyanato groups, some or all of whose H atoms have been substituted by radicals of the formulaxe2x80x94C(O)N(H)-(Alk**)-OC(O)-C(R4)xe2x95x90CR2(R3), wherein (Alk**), R2, R3 and R4 have the meaning given above, particularly 2-isocyanatoethylmethacrylate (IEM).
In step (b) the vinyl monomer having a reactive or crosslinking group may be grafted as such or in admixture with a suitable vinyl co-monomer, preferably a hydrophilic vinyl co-monomer, onto the material surface.
A preferred embodiment of step (b) of the invention concerns co-polymerizing a vinyl monomer comprising a reactive group with a hydrophilic vinyl co-monomer.
Another preferred embodiment of step (b) is the co-polymerization of a vinyl monomer comprising a crosslinkable group, with a hydrophilic vinyl co-monomer.
A suitable vinyl monomer having a reactive group in step (b) independently may be one of the compounds comprising an ethylenically unsaturated group mentioned in step (a) where the above given meanings and preferences apply. A particularly preferred monomer having a reactive group in step (b) is acrylic acid.
Suitable monomers having a crosslinkable group include, without the following being an exhaustive list, difunctionalized active esters, such as ethylene glycolbis[sulfosuccinimidyl-succinate] and bis[sulfosuccinimdyl]suberate, sulfosuccinimidyl[4-azidosalicylamido]hexano-ate, difunctional isocyanates, diacrylates such as 1,4-butanedioldiacrylate or xcex1,xcfx89-PEG-diacrylate and diepoxides such as ethyleneglycoldiglycidylether.
Preferably, the crosslinkable monomer is a monofunctonal vinyl monomer, for example a vinyl monomer comprising an isocyanato, epoxy, hydroxy, amino or carboxy functionality. The crosslinking according to step (d) then may be accomplished through these groups, either by reaction with each other or with other functional groups being present in the polymer. For example, when using a monomer having a hydroxyalkyl group such as N-hydroxymethyl acrylamide, the hydroxyalkyl groups of the resulting polymer may be crosslinked afterwards in an acidic medium. Alternatively, functional groups in the resulting polymer such as those mentioned above may be crosslinked afterwards by adding a co-reactive difunctional compound, for example a diamine such as ethylenediamine, a diol, a polyol or a diisocyanate.
The expression xe2x80x9chydrophilic vinyl co-monomerxe2x80x9d is understood to mean a monomer that typically produces as homopolymer a polymer that is water-soluble or capable of absorbing at least 10% by weight water.
The proportion of vinyl monomers having a reactive group, if used, is preferably from 0.001 to 1 units per unit of hydrophilic vinyl co-monomer, especially from 0.01 to 0.5 units, more preferably from 0.02 to 0.2 units and in particular from 0.02 to 0.1 units. The number of crosslinking monomers, if used, is preferably from 0.001 to 0.1 units per unit of hydrophilic vinyl co-monomer, especially from 0.01 to 0.05 units and most preferably from 0.01 to 0.02 units.
Suitable hydrophilic vinyl co-monomers include, without the following being an exhaustive list, hydroxy-substituted C1-C2-alkyl acrylates and methacrylates, acrylamide, methacryl-amide, N-mono- or N,N-di-C1-C2-alkylacrylamide and -methacrylamide, ethoxylated acrylates and methacrylates, hydroxy-substituted C1-C2-alkyl vinyl ethers, sodium ethylenesulfonate, sodium styrenesulfonate, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrole, N-vinylsuccinimide, five- to seven-membered N-vinyl lactams, 2- or 4-vinylpyridine, amino- (the term xe2x80x9caminoxe2x80x9d also including quatemary ammonium), mono-C1-C2-alkylamino- or di-C1-C2-alkylamino-C1-C2-alkyl acrylates and methacrylates, allyl alcohol and the like. Preferred are acrylamide, N,N-di-C1-C2-alkyl(meth)acrylamides such as N,N-dimethyl acrylamide or five- to seven-membered N-vinyl lactams such as N-vinylpyrrolidone, in particular acrylamide.
The vinyl monomer having a reactive or crosslinking group, optionally in admixture with a hydrophilic vinyl co-monomer, may be applied to the modified material surface and polymerized there according to processes known per se. For example, the material is immersed in a solution of the vinyl monomer(s), or a layer of vinyl monomer(s) is first of all deposited on the modified material surface, for example, by dipping, spraying, spreading, knife coating, pouring, rolling, spin coating or vacuum vapor deposition. Suitable solvents, if used in the polymerization process, are water and, for example, dipolar aprotic solvents such as, for example, acetonitrile. The polymerization of the vinyl monomer(s) on the material surface then may be initiated, for example, thermally by the action of heat or by irradiation, particularly by UV radiation. Suitable light sources for the irradiation are known to the artisan and comprise for example mercury lamps, high pressure mercury lamps, xenon lamps, carbon arc lamps or sunlight. The time period of irradiation may depend, for example, on the desired properties of the resulting composite material but is usually in the range of up to 30 minutes, preferably from 10 seconds to 10 minutes, and particularly preferably from 0.5 to 5 minutes. It is advantageous to carry out the irradiation in an atmosphere of inert gas. After the polymerization, any non-covalently bonded monomers, oligomers or polymers formed can be removed, for example by treatment with suitable solvents.
In case of a thermally initiated polymerization of the vinyl monomer(s) on the material surface said polymerization may be carried out, for example, at elevated temperature, for example at a temperature of from 35 to 100xc2x0 C. and preferably 40 to 80xc2x0 C., for a time period of, for example, from 10 minutes to 48 hours and preferably 30 minutes to 36 hours in the absence or presence of one of the above-mentioned solvents. It is advantageous to carry out the thermally initiated polymerization in an atmosphere of inert gas.
Polymerization initiators are typically those that are initiating a radical polymerization of ethylenically unsaturated compounds. Suitable thermal polymerization initiators are known to the skilled artisan and comprise for example peroxides, hydroperoxides, azo-bis(alkyl- or cycloalkylnitriles), persulfates, percarbonates or mixtures thereof. Examples are benzoylperoxide, tert.-butyl peroxide, di-tert.-butyl-diperoxyphthalate, tert.-butyl hydroperoxide, azo-bis(isobutyronitrile), 1,1xe2x80x2-azo-bis (1-cyclohexanecarbonitrile), 2,2xe2x80x2-azo-bis(2,4-dimethylvaleronitrile), 4,4xe2x80x2-azo-bis(4-cyanovaleric acid and the like.
Initiators for the radiation-induced polymerization may belong to different types, for example to the thioxanthone type and to the benzoin type, particularly benzoinmethylether, 1-hydroxycyclohexylphenyl ketone, Darocure 1173 and Irgacure types.
By means of the polymerization step (b), the vinyl monomer(s) may be grafted to the bulk material surface with formation of a primary coating comprising a plurality of polymer chains bonded to the surface. Each polymer chain contains reactive groups or crosslinking groups at regular intervals (if the vinyl monomer comprising the reactive or crosslinking group is used without a vinyl co-monomer) or statistically distributed (if the vinyl monomer comprising the reactive or crosslinking group is used in combination with a vinyl co-monomer). The reactive groups that are present in the polymer chains are those mentioned before in the description of the vinyl monomers comprising a reactive group.
A suitable further compound comprising an ethylenically unsaturated double bond in step (c) independently may be one of the compounds comprising an ethylenically unsaturated group mentioned in step (a) where the above given meanings and preferences apply. A particularly preferred compound having an ethylenically unsaturated double bond in step (c) is IEM.
A suitable hydrophilic monomer used in step (c) may be one of the hydrophilic vinyl co-monomers mentioned in step (b), wherein the above given meanings and preferences apply.
A suitable crosslinking monomer used in step (c) may be one of the monomers having a crosslinkable group as mentioned in step (b) wherein the above given meanings and preferences apply.
A preferred embodiment of step (c) comprises first of all reacting a compound comprising an ethylenically unsaturated double bond, in particular IEM, with the primary coating obtained according to step (b) and then graft polymerizing a hydrophilic monomer, in particular acrylamide, onto the primary coating.
A further preferred embodiment of step (c) comprises first of all reacting a compound comprising an ethylenically unsaturated double bond, in particular IEM, with the primary coating obtained according to step (b) and then graft polymerizing a mixture of a hydrophilic monomer, in particular acrylamide, and a crosslinking monomer onto the primary coating.
The graft polymerization in step (c) may be accomplished as described in step (b).
One embodiment of the optional step (d) comprises the crosslinking of crosslinkable groups being present on the modified material surface after step (b) or (c) with a difunctional compound selected from the group consisting of diisocyanates, diamines, dioles, 1,4-butanedioldiacrylates and xcex1,xcfx89PEG-diacrylates. A further embodiment of the optional step (d) comprises the crosslinking of crosslinkable groups being present on the modified material surface after step (b) or (c) by means of an addition or condensation reaction.
The coated material obtained according to the invention may be purified afterwards in a manner known per se, for example by washing or extraction with a suitable solvent such as water.
The coating thickness of the coated material surfaces obtained according to the process of the invention depends principally on the desired properties. It can be, for example, from 0.001 to 1000 xcexcm, preferably from 0.01 to 500 xcexcm, more preferably from 0.01 to 100 xcexcm, even more preferably from 0.05 to 50 xcexcm, especially preferably from 0.1 to 5 xcexcm and particularly preferably from 0.1 to 1 xcexcm.
A further embodiment of the invention relates to a material that is coated by the process of the invention.
The material that is coated by the process of the invention is, for example, an organic bulk material, preferably a biomedical device, e.g. an ophthalmic device, preferably a contact lens including both hard and particularly soft contact lenses, an intraocular lens or artificial comea. Further examples are materials useful for example as wound healing dressings, eye bandages, materials for the sustained release of an active compound such as a drug delivery patch, moldings that can be used in surgery, such as heart valves, vascular grafts, catheters, artificial organs, encapsulated biologic implants, e.g. pancreatic islets, materials for prostheses such as bone substitutes, or moldings for diagnostics, membranes or biomedical instruments or apparatus.
The biomedical devices, e.g. ophthalmic devices obtained according to the invention have a variety of unexpected advantages over those of the prior art which make those devices very suitable for practical purposes,e.g. as contact lens for extended wear or intraocular lens.
For example, they do have a high surface wettability which can be demonstrated by their contact angles, their water retention and their water-film break up time or tear film break up time (TBUT).
The TBUT plays an particularly important role in the field of ophthalmic devices such as contact lenses. Thus the facile movement of an eyelid over a contact lens has proven important for the comfort of the wearer; this sliding motion is facilitated by the presence of a continuous layer of tear fluid on the contact lens, a layer which lubricates the tissue/lens interface. However, clinical tests have shown that currently available contact lenses partially dry out between blinks, thus increasing friction between eyelid and the lens. The increased friction results in soreness of the eyes and reduced movement of the contact lenses. Now it has become feasible to considerably increase the TBUT of commercial contact lenses such as, for example, Focus Dailies (trademark), Focus New Vuess or Lotrafilcon A lenses, by applying a surface coating according to the invention. On the base curve of a contact lens, the pronounced lubricity of the coating facilitates the on-eye lens movement which is essential for extended wear of contact lenses. Moreover, the materials obtained by the process of the invention provide additional effects being essential for lenses for extended wear, such as an increased thickness of the pre-lens tear film which contributes substantially to low microbial adhesion and resistance to deposit formation. Due to the extremely soft and lubricious character of the novel surface coatings, biomedical articles such as in particular contact lenses coated by the process of the invention show a superior wearing comfort including improvements with respect to late day dryness and long term (overnight) wear. The novel surface coatings moreover interact in a reversible manner with occular mucus which contributes to the improved wearing comfort.
In addition, biomedical devices, e.g. ophthalmic devices such as contact lenses, coated by the process of the invention, have a very pronounced biocompatibility combined with good mechanical properties. For example, the devices are blood compatible and have a good tissue integration. In addition, there are generally no adverse eye effects observed, while the adsorption of proteins or lipids is low, also the salt deposit formation is lower than with conventional contact lenses. Generally, there is low fouling, low microbial adhesion and low bioerosion while good mechanical properties can be for example found in a low friction coefficient and low abrasion properties. Moreover, the dimensional stability of the materials obtained according to the invention is excellent. In addition, the attachment of a hydrophilic surface coating at a given bulk material according to the invention does not affect its visual transparency.
In summary, the ophthalmic devices obtained by the process of the invention, such as contact lenses and artificial cornea, provide a combination of low spoilation with respect to cell debris, cosmetics, dust or dirt, solvent vapors or chemicals, with a high comfort for the patient wearing such ophthalmic devices in view of the soft hydrogel surface which for example provides a very good on-eye movement of the ohthalmic device. Biomedical devices such as adhesion barriers in tissue surgery, renal dialysis membranes, blood storage bags, pacemaker leads or cardiovascular devices such as heart valves and artificial blood vessels (vascular grafts) coated by the process of the invention resist fouling by proteins, thus reducing the rate and extent of thrombosis. Blood-contacting devices fabricated according to the present invention are therefore haemocompatible and biocompatible. Diagnostics and biosensing applications suffer from reduced signal-to-noise ratios when non-specific protein adsorption occurs; hence, the present coatings offer scope for devices with greater range of sensitivity.
In the examples, if not indicated otherwise, amounts are amounts by weight, temperatures are given in degrees Celsius. Tear break-up time values in general relate to the pre-lens tear film non-invasive break-up time (PLTF-NIBUT) that is determined following the procedure published by M. Guillon et al., Ophthal. Physiol. Opt. 9, 355-359 (1989) or M. Guillon et al., Optometry and Vision Science 74, 273-279 (1997). Average advancing and receding water contact angles of coated and non-coated lenses are determined with the dynamic Wilhelmy method using a Krxc3xcss K-12 instrument (Kruss GmbH, Hamburg, Germany). Welling force on the solid is measured as the solid is immersed in or withdrawn from a liquid of known surface tension.